ATMOSPHERIC RAILWAY, a railway on which the locomotive-power is supplied by the pressure of the atmosphere more or less directly on the carriages themselves. The idea of producing railway locomotion in this manner has been successively prosecuted by Lewis, Medhurst, Valiance, and Pinkus; and latterly with a greater prospect of success by Clegg, in connection with Samuda. Valiance patented a plan which proposed the conveyance of passengers along a railway laid within an air-tight tunnel exhausted in front of a carriage working as a piston, the pressure of the atmosphere acting on the carriage from behind. This plan was made public in 1825, and ultimately brought into experimental operation at Brighton, proving the possibility of such a mode of transit. The general opinion as to its merits was, that though it might succeed in the transmission of goods, or, with a mailer tube than the tunnel, might suit well the conveyance of the mails, it could not be ekpected to enjoy the favor of the traveling public, on account of its dark close tunnel. Thus the subject of atmospheric railways had ceased to attract attention, when the curiosity of the public was again called to it, by the proposal of another plan of propulsion, by Henry I'inkus, an American gentleman, resident in England, who took out a patent for it about the year 1835, under the name of the pneumatic railway. The apparatus for this was to consist of a cast-iron tube of about 40 in. diameter, having a slit of about2 in. wide on its upper side, the slit (which was covered by a flexible flap or valve) furnishing an opening through which the mechanism of a piston working within the tube might be connected with that of the leading carriage without.
Under improved arrangements of the details, Messrs. Clegg and Samuda made an I experiment of this plan in 1840, on a part of the line of the WestLondon railway; and 1 so favorable was the issue, that the directors of the Dublin and Kingstown railway adopted the atmospheric pressure system for a projected extension of their line from Kingstown to Dalkey. Accordingly, parliamentary sanction was obtained for the line, and the first A. R. was in full operation at the beginning of the year 1844. In that year the London and Croydon railway company began to lay down a !irk of A. R. alongside of their locomotive line from London to Croydon. The South Devon railway company also adopted the atmospheric mode of working on a part of their railway. Both of these lines, however, were shortly afterwards abandoned as unsatisfactory.
The result of these trials has clearly shown that the A. R. system cannot stand in competition with that of the locomotive engine, unless, perhaps, in some very peculiar situation. The expense and care necessary to keep the tube with its valve in good working-order, led to the removal of the atmospheric mechanism from the various railways on which it was established; so that the history of A. R. may be ranked under the chapter of failures. They survive only in the form of pneumatic dispatch tubes, which are used largely in London (in connection principally with the telegraph service), for the conveyance of parcels of messages for short distances.